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Does lesion in a pathway cause an ipsolateral or contralateral effect?
The reference point is always the lesion
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Which types of neurons are damaged and where are they located in the spinal cord?
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What modalities would be lost?
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Where would the loss of modalities occur?
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Where does decussation occur?
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Where do 1st order sensory neurons originate?
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Where do 2nd order sensory neurons originate?
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Where do 3rd order sensory neurons originate?
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Which neurons pass through the internal capsule?
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Understand that all sensory info must be processed by the thalamus (except smell)...
before you can consciously perceive it
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All sensory info can be responded to reflexively at the spinal cord or the brain stem level w/o being:
consciously perceived.
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What is the pathway of information?
external energy-->receptors on distal ends of sensory neurons-->action potentials-->afferent sensory neurons of PNS
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What are the types of external energy?
- thermal
- electrical
- mechanical
- chemical
- electromagnetic
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What happens at the receptors on distal ends of sensory neurons?
transduction of energy
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What type of process are action potentials?
electrochemical
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What are some examples of afferent sensory neurons of the PNS?
- cranial and spinal nerves
- nociceptors
- mechanoreceptors
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For the purpose of sensory pathways, what is considered general sensation?
- conscious proprioception
- two-point discrimination
- fine touch
- crude touch
- nociception
- temperature
- vibration
- movement sense
- stereognosis
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How many general sensations apply to somatic receptive fields?
all
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How many general sensations apply to visceral receptive fields?
most except for two-point discrimination, stereognosis, conscious proprioception
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What is the spinothalamic tract responsible for?
noxious stimulation, pain, temperature, crude touch
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Where does the spinothalamic tract receive input from?
UE, LE, trunk, abdomen, and pelvis
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As the spinothalamic tract ascends the spinal cord, it adds more and more:
2nd order sensory neurons
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Is the spinothalamic tract larger at the bottom or the top?
top
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Where are 1st order neurons of the spinothalamic tract located?
in spinal nn or nerves of ANS
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What type of receptive fields are found in the 1st order neurons of the spinothalamic tract?
somatic and visceral
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What are found in the 1st order neurons of the spinothalamic tract?
cell bodies in DRG of spinal nerves
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What do 1st order neurons of the spinothalamic tract synapse with?
2nd order in dorsal horn; may or may not synapse w/ interneurons
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Where do 2nd order neurons of the spinothalamic tract decussate?
immediately at point of entry to contralateral side and ascend as spinothalamic tract
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What do the 2nd order neurons of the spinothalamic tract become?
spinal lemniscus
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When do the 2nd order neurons of the spinothalamic tract become the spinal lemniscus?
upon entry to the tegmentum of the brainstem
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After the spinal lemniscus continues through the tegmentum it terminates w/:
thalamus at ventral posterior lateral nucleus (VPL=R nucleus)
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Where do 3rd order neurons of the spinothalamic tract synapse?
b/w 2nd and 3rd order in thalamus
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Where do 3rd order neurons of spinothalamic tract ascend?
through internal capsule to terminate in postcentral gyrus of parietal lobe
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What modalities are lost if spinothalamic tract is cut?
- lose perception (pain, temp, crude touch) of contralateral side below level of lesion, if tract is cut once it enters spinal cord
- lose perception of ipsilateral side if tract is cut at a spinal nerve
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It is called the spinothalamic tract of the left side of the spinal cord
NOT the left spinothalamic tract!!
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What is the dorsal column system responsible for?
- conscious proprioception
- two-point discrimination
- vibration
- movement sense
- fine touch
- stereognosis
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Where are 1st order sensory neurons found?
spinal nerves
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Where are the cell bodies of the 1st order neurons of the dorsal column system?
dorsal root ganglion (DRG)
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Where are the receptors of the dorsal column system found?
- skin
- subcutaneous tissue
- muscle
- tendon
- joints
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What structure does the 1st order neurons of the dorsal column system enter?
dorsal horn
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Do the 1st order neurons of the dorsal column system decussate?
no
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Where does the 1st order neuron of the dorsal column system ascend?
ipsilaterally in dorsal white column to medulla
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Fasciculus gracilis:
1st order from LE that synapses w/ nucleus gracilis in tegmentum of the medulla (medial)
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Fasciculus cuneatus:
1st order from UE that synapses w/ nucleus cuneatus in tegmentum of the medulla (lateral)
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Where do the 2nd order neurons of dorsal column system decussate?
in medulla
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When the 2nd order neuron of the dorsal column system decussates in the medulla it collectively forms what?
medial lemniscus
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Where does the 2nd order neurons of the dorsal column system ascend?
to tegmentum of brainstem
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Where does the 2nd order neurons of the dorsal column system terminate?
ventrobasal nucleuar complex of thalamus
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What do 2nd order neurons of the dorsal column system synapse with?
3rd order neurons in thalamus
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What structure does the 3rd order neuron of the dorsal column system pass through?
internal capsule
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After passing through the internal capsule where does the 3rd order neuron of the dorsal column system go?
to postcentral gyrus of parietal lobe
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What does the 3rd order neuron of dorsal column system do once in the postcentral gyrus of parietal lobe?
- allows:
- conscious proprioception
- two-point discrimination
- vibration
- movement sense
- fine touch
- stereognosis
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What modalities are lost if the dorsal column system is cut?
- loss on ipsilateral side if cut at or before the medulla (dorsal column of SC)
- loss on contralateral side if cut after the medulla (ex: if lesion is in pons)
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What is the spinocerebellar tract responsible for?
unconscious proprioception
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Where are the 1st order neurons of the spinocerebellar tract located?
spinal nn
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Where are the cell bodies of the 1st order neurons of the spinocerebellar tract?
DRG
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Where are the receptors of the 1st order neurons of the spinocerebellar tract?
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Where do the 1st order neurons of the spinocerebellar tract terminate?
dorsal horn (specifically lamina VII --aka Nucleus dorsalis or Clarke's nucleus) to synapse w/ 2nd order
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What are the 2nd order neurons of spinocerebellar tract associated w/?
T1-L2 levels
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What two tracts are there with the 2nd order neurons of spinocerebellar tract?
anterior and posterior
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Does the posterior spinocerebellar tract decussate?
no
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The posterior spinocerebellar tract enters what?
cerebellum via inferior cerebellar peduncle
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Why does the posterior spinocerebellar tract enter the cerebellum?
to relay info from LE
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Does the anterior spinocerebellar tract decussate?
yes, at point of entry
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The anterior spinocerebellar tract enters what?
cerebellum via superior cerebellar peduncle (superior is primarily efferent--though anterior spinocerebellar tract is an exception to this rule)
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Lesions of the 2nd order neurons of the spinocerebellar tract result in:
loss of motor control (but this is more finesse type so less noticeable clinical symptoms)
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